The present invention relates to an angular measurement system having an integrated Ferraris sensor.
Angular measurement systems having an integrated Ferraris sensor unite the advantage of precise (angular) position measurement with the direct measurement of angular acceleration or angular velocity, which otherwise is only obtained from the positional signal in a time-differentiation operation. When a positional signal is differentiated, small interferences in the positional signal lead, however, to substantial changes in the differentiated signal, and thus in the calculated angular velocity and angular acceleration. This effect does not occur when a direct measurement of the angular acceleration is taken using a Ferraris sensor. Rather, the angular velocity can be obtained from an integration of the angular acceleration signal. Interferences in the angular acceleration signal are even smoothed in the process.
Ferraris sensors detect the magnitude of or the change in eddy currents, which arise due to the relative motion of magnetic fields and eddy current bodies.
European Published Patent Application No. 0 661 543 describes an angular measurement system, in which the angular acceleration is also measured. For this, two signalers are interconnected in a torsionally rigid manner, and a signal-detection unit is assigned to each signaler. A first of the two signalers is implemented by an optical or inductive graduation, which is scanned by a signal-detection unit having an optical or inductive scanning head. A second signaler is composed of an electrically conductive disk which is traversed in a perpendicular direction by a magnetic flux. This magnetic flux can be generated by suitable magnets. If the disk is moved in relation to the magnet, eddy currents form, which, in turn, produce a magnetic field. The change in this magnetic field is sensed by a signal-detection unit, so that the measured quantity ascertained in the signal-detection unit represents a measure for the angular acceleration. The two signalers are either each joined in the form of a separate disk, in a torsionally rigid manner, to a shared shaft, or the first signaler is mounted directly at the outer edge of the second signaler, thereby altogether enlarging the disk diameter.
In the foregoing, where two signalers are combined to form one disk, problems arise due to the different thermal expansion of the materials used when the angular measurement system is intended to be used at different temperatures. The connection of the two graduated disks or disk rings can loosen, for example, due to a greater expansion of the outer ring.
It is therefore an object of the present invention to provide an angular measurement system having an integrated Ferraris sensor, which may ensure that the signalers used are held securely together, even given different operating temperatures.
To join the signalers, the present invention provides for relief elements, which also may ensure a secure cohesion of the signalers, even given a different thermal expansion. In this context, the materials employed for the signalers and the relief elements may be selected such that the strain between the signalers is held constant in response to varying temperatures.
Further advantages of the present invention and details pertaining thereto are derived from the following description of example embodiments, on the basis of the figures.